Safety razors

ABSTRACT

A safety razor blade unit has a guard ( 2 ), a cap ( 3 ) and three parallel blades ( 11, 12, 13 ) mounted between the guard and cap, at least one of the blades, guard and cap being movable from an at rest (non-shaving) position to modify a blade exposure dimension to attain a target blade geometry, at which shaving is initiated, in which the exposure of the first blade ( 11 ) is not greater than zero and the exposure of the third blade ( 13 ) is not less than zero. At least one of the cap ( 3 ) and guard ( 2 ) can be movable against the force of a spring ( 21  or  20 ) from an at rest position in which all the blades between the guard and cap have their cutting edges disposed below a plane tangential to the skin contacting surfaces of the guard and cap. The blades can be independently sprung or carried for movement in unison on a carrier pivotally mounted in a frame of the blade unit.

This invention relates to safety razors and is particularly concernedwith safety razors having blade units with a plurality of bladesdefining parallel sharpened edges arranged to pass in succession over askin surface being shaved. The invention is applicable to safety razorshaving their blade units permanently attached to the razor handle, andto safety razors having their blade units detachably mounted on thehandle for replacement when the blade edges have become dulled, and ineither case the invention can be incorporated whether the blade unit isimmovably mounted to the handle or mounted to move, e.g., to pivot aboutan axis parallel to the blade edges, relative to the handle under theinfluence of forces imparted on the blade unit during shaving.

The present invention has specific reference to safety razor blade unitsincorporating three blades, and the relative positioning of the bladeedges. Our prior patent application No. PCT/US94/10717 teaches that withsuch blade units an improved overall shaving performance can be achievedwhen the blade edges are set according to a particular geometricalpattern, namely with the first blade, which has its edge nearest theguard, having an exposure not greater than zero, and the third blade,which defines the edge nearest the cap, having an exposure not less thanzero. In the most efficacious geometrical arrangement, the first orprimary blade has a negative exposure with an absolute value in therange of 0 to 0.2 mm, preferably equal to about −0.04 mm for a primaryblade span of around 0.7 mm, the third blade has an exposure with apositive value not greater than about +0.3 mm (preferably less than +0.2mm), for example around +0.06 mm or +0.09 mm, and the second blade hasan exposure of about zero, the second and third blade spans each being1.0 to 2.0 mm, preferably about 1.5 mm. For convenience the geometricalarrangements described and claimed in the aforementioned priorapplication are referred to herein as “the target geometry for theblades”. For further information and details of the blade geometryreference may be made to the earlier application the contents of whichare incorporated herein by this reference.

The blade exposure is defined to be the perpendicular distance or heightof the blade edge measured with respect of a plane tangential to theskin contacting surfaces of the blade unit elements next in front of andnext behind the blade edge. This can be a positive number if the bladeedge is above this plane i.e., closer to the skin surface to be shavedthan the tangential plane, or a negative number if the blade edge isbelow this tangent plane, i.e., further away from the skin than thetangent plane. The span of a blade is the distance from the blade edgeto the skin contacting element immediately in front of that edge asmeasured along a tangent line extending between said element and theblade edge.

The three-blade geometry specified above is applicable to a blade unitin which the blades are immovably mounted relative to the guard and cap.It also applies to the initial or at rest geometry in the case of ablade unit in which the blades are spring mounted and capable of beingdeflected under the forces applied to the blades during shaving.

The present invention, recognizes that it may be desirable for someparts of a blade unit to be movable relative to other parts and thatthis may be accommodated without forfeiting the advantages of the bladegeometry discussed above. Thus, according to a preferred embodiment ofthe present invention there is provided a safety razor blade unitcomprising a guard, a cap, and first, second and third blades withparallel sharpened edges located in sequence between the guard and cap,at least one element selected from the blades, guard and cap beingmovable from a non-shaving position (i.e., at rest position not loadedby shaving forces) to modify a blade exposure dimension of the bladeunit and to attain a modified blade geometry (also referred to as thetarget geometry) wherein the exposure of the first blade is not greaterthan zero and the exposure of the third blade is not less than zero, atleast one of the first and third blades having a different exposure whenthe at least one movable element is in the non-shaving position.

The at least one element can be lightly biased, such as by means of aspring, to an initial, non-shaving (at rest) position at which thetarget geometry of the blades does not apply, but when the blade unit isapplied to the skin during shaving the at least one element can bedisplaced to a position in which the target geometry of the blades isattained.

The at least one element can comprise the guard and/or the cap and/orone or more of the blades.

In accordance with another aspect the present invention provides asafety razor blade unit comprising a guard, a cap and a plurality ofblades with a parallel sharpened edges located in succession between theguard and cap, at least one of the guard and cap being movable against aspring force from a non-shaving (at rest) position to a predeterminedoperable position in which a modified blade geometry target geometry isobtained, in the non-shaving position the blade edges being disposedbelow a plane tangential to the skin contacting surfaces of the guardand cap.

A full understanding of the invention will be gained from the followingdetailed description in which reference is made to the accompanyingdrawings, wherein:

FIG. 1 illustrates a preferred blade geometry during shaving andcorresponds to FIG. 2 of earlier application No. PCT/US94/10717;

FIG. 2 is a transverse cross-section through a first embodiment of thepresent invention when not in use;

FIG. 3 shows the blade unit of FIG. 2 with the parts occupying differentrelative positions;

FIGS. 4 and 5 are views corresponding to FIGS. 2 and 3, respectively andshowing a second embodiment of the invention; and

FIGS. 6 and 7 are views corresponding to FIGS. 2 and 3 and illustratinga third embodiment of the invention.

FIGS. 8-10 are illustrations of different orientations of a cartridgewith respect to a shaver's skin.

FIG. 11 is a cross-section through a further embodiment showing the useof cantilever arms for spring mounting of blades.

FIG. 1 illustrates schematically a safety razor blade unit having aframe 1 defining a guard 2 and a cap 3 and mounting a lubricating strip4. Supported by the frame and carried by respective support members area primary blade 11, a secondary blade 12 and a tertiary blade 13, theblades having their edges lying in a common plane P. The target geometryof the blade unit is as follows:

a) The span S₁ of the primary blade 11 is 0.5 to 1.5 mm, and ispreferably 0.7 mm;

b) The span S₂ of the secondary blade 12 and the span S₃ of the tertiaryblade 13 are in the range of 1.0 to 2.0 mm, and each is preferably 1.5mm;

c) The distance S₄ from the edge of the tertiary blade to the cap isabout 1.80 mm;

d) The exposure of the primary blade is −0.04 mm;

e) The exposure of the secondary blade 12 is not less than the exposureof the primary blade 11 and not greater than the exposure of thetertiary blade 13 and, as shown, is equal to zero;

f) The exposure of the tertiary blade is about +0.09 mm.

Except as otherwise noted, the embodiments of the present inventiondescribed below are so arranged that a substantially similar bladetarget geometry can be achieved although such geometry does not applywhen the blade unit is at rest and not in use (i.e., a non-shavingposition not loaded by shaving forces).

In the blade unit shown in FIGS. 2 and 3, the guard 2 is mounted to theframe for up and down sliding movement between upper and lower endpositions defined by stop surfaces provided on the frame. The guard isurged lightly to the upper end position by a spring 20. The cap 3 issimilarly slidably mounted by the frame for up and down movement betweenend positions defined by stops, and a spring 21 lightly biases the capto its upper end position. In the upper end position of the guard anupwardly facing shoulder 30 on the guard abuts a stop surface 31 definedby a flange 32 integral with the frame, as seen in FIG. 2. Similarly, inthe upper end position of the cap an upwardly facing shoulder 34 on thecap abuts a stop surface 35 defined by a flange 36 integral with theframe. In the lower end positions of the guard and cap, the guard andcap respectively abut stop surfaces 37 and 38 defined by a bottom wallportion of the frame, as shown in FIG. 3. The three blades 11, 12, 13,can be stationarily mounted in the frame or can be biased by respectivesprings against a stop surface 18 defined by inturned flanges on the endwalls of the frame. In the out of use condition, the blade geometry isoutside the target geometry for the blades. The negative exposure of theprimary blade has an absolute value significantly greater than 0.2 mmand the tertiary blade has a negative exposure. In use, the guard andcap can be depressed against the springs 20, 21 which act respectivelythereon and occupy their lower end positions, as shown in FIG. 3, whenin the start-shaving disposition a modified geometry (i.e., the targetgeometry) substantially corresponding to that of FIG. 1 is obtained.From this target geometry the blades may be deflected downwardly againsttheir individual springs 19, but the enhanced shaving performance due tothe target geometry need not be lost. Furthermore, it is not essentialthat the guard and cap remain in their lower end positions when they arein contact with the skin in use of the blade unit and they can bepermitted to move under the influence of their respective springs 20,21.

In the embodiment of FIGS. 4 and 5, the cap 3 and guard 2 are fixed tothe frame as in FIG. 1, but the blades in this case are movable andinfluenced by respective springs 24. The springs could press the bladeslightly upwardly against a stop surface (as mentioned in relation toFIGS. 2 and 3) but as shown the springs are unstressed when the bladeunit is at rest and not in use so there is no preload on the blades. Inthis condition of the blade unit the target geometry for the blades isnot satisfied, e.g., because the primary blade has a positive exposure,and the exposure of the tertiary blade is greater than the preferredmaximum of +0.2 mm. In use, however, the blades are depressed againstthe force of the springs so that a modified geometry is obtained, asshown in FIG. 5, and substantially the target geometry of FIG. 1 can beobtained. If required the blades could be provided with stops topredetermine the positions to which they need to be deflected to reachthe target geometry. Alternatively, the spring rates can be chosen sothat deflection from positions according to the target geometry will notbe excessive.

The embodiment of FIGS. 6 and 7 also has a stationary guard 2 and cap 3.The three blades 11, 12, 13 are mounted on a rocker unit 26 supported inthe frame 1, such as by a shell bearing, for pivotal movement of theblades in unison about a pivot axis A located above the blade edges. Aleaf spring 28 carried by the frame acts on the rocker urging it lightlyto the non-shaving (i.e., at rest) position shown in FIG. 6, at whichthe blades are outside the target geometry for the blades, the primaryblade having a positive exposure and the tertiary blade having anegative exposure. In use, forces applied will cause the rocker unit 26to pivot against the action of the spring 28 and to take up the positionwhich is shown in FIG. 7 and which may be predetermined by a stop fixedon the frame such as stop 40 or stop 41 indicated schematically in thedrawings. In this condition of the blade unit the geometry issubstantially as specified above in relation to FIG. 1, and hence thetarget geometry for the blades applies. As illustrated, the blades arefixedly mounted on the rocker but the blades may be mounted on therocker by springs so that during shaving the blades may become deflectedfrom the target geometry, as mentioned above in relation to FIGS. 2 and3.

It will be understood that although in the at rest postion they do notinitially satisfy the geometrical parameters to obtain the best shavingperformance, all of the embodiments are adapted Do that thesegeometrical parameters will be obtained in use. While some embodimentshave been described it will be appreciated that others are also possiblewithin the scope of the claims. For example, just one of the guard andcap could be movable, or the blades and the guard and/or cap could bemovable, or just one or two of the blades could be movable. Othercombinations of movable elements are also possible. Futhermore, theelements could be adapted to move in a different manner, such as by theguard being arranged to flex or tilt and/or to move to vary the span ofthe primary blade as well as modify the blade exposure.

A feature of the guard and/or cap being movable and sprung as in theembodiment of FIGS. 2 and 3 is that when not in use the blade edges areall disposed below a plane tangential to the skin contacting surfaces ofthe guard and cap. However, the guard and/or cap can be readilydisplaced to the retracted position defined by a stop so that a desiredtarget blade geometry is obtained.

It is believed that beneficial shaving results are achieved whencartridges with three resiliently mounted blades exhibit, duringshaving, a “progressive force” pattern, i.e. the force on the tertiaryblade is greater than the force on the primary blade and the force onthe secondary blade is intermediate to the forces on the primary andtertiary blades or equal to the force on either the tertiary or theprimary blade. The force pattern on the blades can be influenced by thecartridge orientation bias effect, blade geometry, and blade springarrangement, as is discussed in detail below.

The cartridge orientation bias effect relates to how the angularorientation of the cartridge with respect to the skin surface influencesthe forces on the individual blades. FIGS. 8-10 illustrate threecartridge orientations, a neutral orientation, a cap-heavy orientation,and a guard-heavy orientation. In these figures, cartridge 130 isillustrated schematically to include a guard 132, cap 134 and blades136, 138, 140 and is shown with a cartridge orientation relative to theskin surface 142 before the skin surface has been deflected. Duringactual shaving, the cartridges would in general be pushed into the skinsurface, deflecting it so that the entire top part of the cartridge willcontact the skin. If it is assumed that the exposures at rest(non-shaving condition), spring preloads and spring rates are equal foreach of the blades, then the cartridge orientation will control theforce pattern on the blades during shaving.

In FIG. 8, the cartridge 130 is oriented in the neutral condition. Inthis case, as the cartridge 130 is pressed against the skin surface 142by the user to bring all of the blades into shaving contact, the forcesare applied uniformly to the three blades. To produce a progressiveforce pattern, the blade geometry and/or the blade spring arrangementcan be modified, as discussed in detail below.

In FIG. 9, the cartridge 130 has a cap-heavy orientation. In this case,the cap 132 contacts the skin surface initially. As the remainder of thetop part of the cartridge is pushed against the skin, more force isapplied to the blades near the cap. Accordingly, the force on thetertiary blade is greater than the force on the secondary blade, whichis greater than the force on the primary blade, which is a progressiveforce pattern.

In FIG. 10, the cartridge 130 has a guard-heavy orientation. In thiscase, the guard 134 contacts the skin surface initially. As theremainder of the top part of the cartridge is pushed against the skin,more force is applied to the blades near the guard. Accordingly, theforce on the primary blade is greater than the force on the secondaryblade, which is greater than the force on the tertiary blade. Theguard-heavy condition thus promotes the opposite of “progressive force.”To produce a progressive force pattern, the blade geometry and/or theblade spring arrangement can be modified to counteract the force patternthat would otherwise be caused by the guard heavy condition, asdiscussed in detail below.

For cartridges that are not pivotally connected to the handle, thecartridge orientation with respect to the skin, and thus the cartridgeorientation bias effect, is generally determined by the orientation ofthe cartridge with respect to the handle. For cartridges attached to thehandle through a pivot, in addition to the at rest orientation of thecartridge, the pivot location and return spring force will affect thecartridge orientation bias effect. For example, if the at rest cartridgeorientation is as shown in FIG. 9, the cap will initially contact theskin; hovever, if the pivot is in the region of the guard, and there islight return spring force, the cartridge will become guard heavy duringshaving.

As noted above, the force pattern on the blades can also be influencedby the blade geometry and blade spring arrangement. The blade geometryrefers to the exposure at rest. The blade spring arrangement refers tothe spring rate and preload.

FIG. 11 illustrates one way of providing resilient mounting for theblades and how at rest exposure of a blade can be adjusted. (Otherspring mounting approaches can also be used.) Referring to FIG. 11,cantilevered plastic arm 144 extends in from housing side wall 146 andprovides resilient support for the bent upper portion 146 at one end ofthe blade. The cutting edge 150 of the blade is prevented from furtherupward movement by metal clip 152, which is secured to the housing. Asimilar arm extends in from the other side of the cartridge and providesresilient support for the other end of the blade under a similarretaining clip. The pair of arms 144 corresponds to springs 19, 24 shownin FIGS. 2-5. The upward force F that arm 144, acting as a cantileveredbeam, exerts on blade portion 148 is a linear function of its downwarddisplacement, y, from its unbiased position: F=k*y, where k is a springconstant that depends upon the length of the arm, L, the moment ofinertia of the arm, I, and the modulus of elasticity, E (k=L³/(3EI)). Ifarm 144 is deflected a distance y_(p) by clip 152 in manufacture (i.e.,providing arm 144 with a preload force F_(p) of k*y_(p)) then y in theformula equals y_(p)+y_(d), where y_(d) equals the movement downwardfrom the at rest position shown in FIG. 11.

The forces on the blades can be controlled in a variety of ways to causea progressive force pattern during shaving. E.g., arm 144 can beprovided with a different spring constant by changing the length of arm144 or the moment of inertia (e.g., by providing a thicker cross-sectionfor arm 144). Arm 144 can also be provided with a different preloadforce F_(p) by keeping the same arm section and length, but moving thelocation at which the arm 144 is attached to housing side wall 146upward (to increase preload force) or downward (to decrease preloadforce). The position or shape of clip 152 could also be adjustedrelative to the arms to adjust preload force F_(p); e.g., clip 152 couldbe mounted so that the portion contacting one blade is lower or higherthan the portion contacting a different blade.

One way to achieve a progressive force pattern during shaving is to havean initial progressive exposure and the same preload force and springconstant for all blades. Another way to achieve a progressive forcepattern during shaving is to have the same initial exposure (e.g., allzero) and to have progressive preload. A progressive preload can beprovided by having the spring constant for the tertiary blade be higherthan the spring constant for the second blade, and by having the springconstant for the primary blade be less than the spring constant for thesecond blade. A progressive preload can also be achieved by using thesame arms (i.e., same spring constants) for all blades, but having thesecond arm mounted higher than the primary blade and the third armmounted higher than the second.

The springs, preloads and initial exposures can be used in combinationwith the cartridge orientation bias effect to produce progressiveexposure and/or a progressive force pattern. For example, if thecartridge has a guard-heavy orientation (e.g., a cap first orientationthough with a pivot in the proximity of the guard and a light returnspring, as noted above), progressive geometry in use can be effectedwith higher preloads, spring constants, and at-rest exposures on thetertiary and secondary blades than on the primary blade. Othercombinations that can be used to promote a progressive force duringshaving include a higher preload, spring constant, or at rest exposureon the third blade than on the first blade or combinations of theseparameters having higher values on the third blade as compared to thefirst blade. Preferably the second blade would have intermediate valuesor values that are the same as the third blade in order to promote theprogressive force pattern.

The spring preloads are typically in the range of about 25 g or less.The force on the individual blades would be expected to be in the rangeof about 0-40 g, with between zero and 20 gms on the first blade, andbetween greater than zero and less than 40 gms on the third blade.Typically the forces on the individual blades would be greater than 5gm. At rest exposures and exposures during shaving typically are in theranges noted earlier.

What is claimed is:
 1. A safety razor blade unit comprising a guard, acap, and first, second and third parallel blades each with sharpenedcutting edges located between the guard and cap, said third blade beingnearer the cap than is said first blade, at least one element selectedfrom the three blades, the guard and the cap being movable against aspring bias, in response to a user bringing the razor blade unit intocontacting relation with skin to be shaved, from an at-rest positionunloaded by externally applied forces to a depressed start-shavingposition to modify a blade exposure dimension of the blade unit and atin said depressed position a target blade geometry, wherein in saidtarget geometry the exposure of the first blade is less than zero andthe exposure of the third blade is greater than zero, at least one ofthe first and third blades having a different exposure when tXe at leastone movable element is in the at-rest position, and wherein when saidfirst and third blades are depressed by an equal amount, the forceexerted on said first blade is less than the force exerted on said thirdblade, and said spring bias biasing the at least one element to theat-rest position upon removal of externally applied forces, and thethree blades being independently mounted for spring-biased movement sothat during shaving the blade movement from respective shaving positionsis translational without changing respective blade angles.
 2. A safetyrazor blade unit according to claim 1, wherein the at least one elementis movable from the non-shaving position to the depressed positiondefined by a displacement limiter applying a force opposing furthermotion in the displacement direction.
 3. A safety razor blade unitaccording to claim 1, wherein in said target blade geometry the spanbetween the first blade edge and the guard is substantially equal to 0.7mm.
 4. A safety razor blade unit according to claim 1, wherein the atleast one movable element is biased by the spring to an end positiondefined by a stop.
 5. A safety razor blade unit according to claim 1,wherein the at least one movable element comprises the guard.
 6. Asafety razor blade unit according to claim 1, wherein the at least onemovable element comprises the cap.
 7. A safety razor blade unitaccording to claim 1, wherein in said target blade geometry the secondblade has an exposure not less than the exposure of the first blade andnot greater than the exposure of the third blade.
 8. A safety razorblade unit according to claim 7, wherein in said target blade geometrythe exposure of the second blade is substantially equal to zero.
 9. Asafety razor blade unit according to claim 1, wherein in said targetblade geometry the span between the edge of the third blade and the edgeof the second blade is in the range of 1.0 and 2.0 mm.
 10. A safetyrazor blade unit according to claim 9, wherein in said target bladegeometry the span between the edges of the first and second bladesand/or between the edges of the second and third blades is substantiallyequal to 1.5 mm.
 11. A safety razor blade unit according to claim 1,wherein in said target blade geometry the exposure of the third bladehas a positive value substantially equal in magnitude to the negativevalue of the exposure of the first blade.
 12. A safety razor blade unitaccording to claim 1, wherein in said target blade geometry the spanbetween the first blade edge and the guard is substantially smaller thanthe span between the edges of the first and second blades and the spanbetween the edges of the second and third blades.
 13. A safety razorblade unit according to claim 1, wherein in said target blade geometrythe span between the edge of the second blade and the edge of the firstblade is in the range of 1.0 to 2.0 mm.
 14. A safety razor blade unitaccording to claim 1, wherein in said target blade geometry the exposureof the first blade has a negative exposure with an absolute value in therange of 0 to 0.2 mm.
 15. A safety razor blade unit according to claim14, wherein in said target blade geometry the span between the firstblade edge and the guard is in the range of 0.5 mm to 1.5 mm.
 16. Asafety razor blade unit according to claim 14, wherein in said targetblade geometry the exposure of the first blade is substantially equal to−0.04 mm.
 17. A safety razor blade unit according to claim 1, wherein insaid target blade geometry the exposure of the third blade has apositive value not greater than +0.3 mm.
 18. A safety razor blade unitaccording to claim 1, wherein in the at-rest positions the third bladehas a more positive exposure than the first blade.
 19. A shavingcartridge comprising a housing having connecting structure adapted tomake a removable connection to a handle, a guard at the front of thecartridge, a cap at the back of the cartridge, and first, second andthird parallel blades each with sharpened skin-contacting cutting edgeslocated on said housing between said guard and cap and independentlymounted for spring-biased movement with respect to said housing, saidthird blade being nearer the cap than is said first blade, said bladesbeing movable from initial at-rest positions determined by respectiveexposures of the blades to shaving positions, wherein said third bladehas a higher preload than said first blade, such that when said firstand third blades are depressed by an equal amount, the force exerted onsaid first blade is less than the force exerted on said third blade. 20.The cartridge of claim 19, wherein said second blade has a higherpreload than said first blade.
 21. The cartridge of claim 19, whereinsaid third blade further has a higher exposure at rest than said firstblade.
 22. The cartridge of claim 19, wherein said third blade furtherhas a higher spring constant than said first blade.
 23. The cartridge ofclaim 19, wherein said third blade further has a higher exposure at restand higher spring constant than said first blade.
 24. The cartridge ofclaim 19, wherein said second and third blades have higher exposure atrests than said first blade and said second blade also has a higherpreload than said first blade.
 25. The cartridge of claim 19, whereinsaid second and third blades have higher spring constants than saidfirst blade and said second blade also has a higher preload than saidfirst blade.
 26. The cartridge of claim 19, wherein said second andthird blades have higher exposure at rests and higher spring constantsthan said first blade and said second blade also has a higher preloadthan said first blade.
 27. A shaving cartridge comprising a housinghaving connecting structure adapted to make a connection to a handle, aguard at the front of the cartridge, a cap at the back of the cartridge,and first, second and third parallel blades each with sharpenedskin-contacting cutting edges located on said housing between said guardand cap and independently mounted for spring-biased movement withrespect to said housing, said third blade being nearer the cap than issaid first blade, said blades being movable from initial at-restpositions determined by respective exposures of the blades to shavingpositions, the three blades being mounted so that during shaving theblade movement from respective shaving positions is translationalwithout changing respective blade angles, wherein when said firstand-third blades are depressed by an equal amount, the force exerted onsaid first blade is less than the force exerted on said third blade. 28.A safety razor blade unit according to claim 27, wherein in the at-restpositions the third blade has a more positive exposure than the firstblade.
 29. The cartridge of claim 27, wherein said housing has pivotingstructure for providing pivoting of said housing about a pivot axis. 30.The cartridge of claim 29, wherein said pivot axis is in front of bladesin the region of said guard.
 31. The cartridge of claim 27, wherein saidthird blade has a higher exposure at rest and a higher spring constantthan said first blade.
 32. The cartridge of claim 27, wherein saidsecond and third blades have higher exposure at rests and higher springconstants than said first blade.
 33. The cartridge of claim 27, whereinthe preload force on said first blade is between zero and 20 gms and thepreload force on said third blade is greater than zero and less than 40gms.
 34. The cartridge of claim 27, wherein said third blade has ahigher spring constant than said first blade.
 35. The cartridge of claim27, wherein said third blade has a higher exposure at rest than saidfirst blade.
 36. The cartridge of claim 27, wherein when all of saidthree blades are depressed by an equal amount the force on the firstblade is less than the force on the second blade, and the force on thesecond blade is less than or equal to the force on the third blade. 37.The cartridge of claim 36, wherein said second and third blades havehigher spring constants than said first blade.
 38. The cartridge ofclaim 36, wherein said second and third blades have higher exposure atrests than said first blade.
 39. A shaving razor comprising a handle, ahousing having connecting structure adapted to make a removableconnection to the handle, a guard at the front of the cartridge, a capat the back of the cartridge, and first, second and third parallelblades each with sharpened skin-contacting cutting edges located on saidhousing between said guard and cap and independently mounted forspring-biased movement with respect to said housing, said third bladebeing nearer the cap tan is said first blade, said blades being movablefrom initial at-rest positions determined by respective exposures of theblades to shaving positions, wherein said third blade has a higherpreload than said first blade, such that when said first and thirdblades are depressed by an equal amount, the force exerted on said firstblade is less than the force exerted on said blade.
 40. The cartridge ofclaim 39, wherein said third blade further has a higher exposure at restthan said first blade.
 41. The cartridge of claim 39, wherein saidsecond blade has a higher preload than said first blade.
 42. Thecartridge of claim 39, wherein said third blade further has a higherspring constant than said first blade.
 43. The cartridge of claim 35,wherein said third blade further has a higher exposure at rest andhigher spring constant than said first blade.
 44. The cartridge of claim39, wherein said second and third blades have higher exposure at reststhan said first blade and said second blade also has a higher preloadthan said first blade.
 45. The cartridge of claim 39, wherein the threeblades are mounted for the independent spring-biased movement so thatduring shaving the blade movement from respective shaving positions istranslational without changing respective blade angles.
 46. Thecartridge of claim 39, wherein said second and third blades have higherspring constants than said first blade and said second blade also has ahigher preload than said first blade.
 47. The cartridge of claim 39,wherein said second and third blades have higher exposure at rests andhigher spring constants than said first blade and said second blade alsohas a higher preload than said first blade.
 48. A safety razor bladeunit comprising a guard a cap and at least three parallel blades eachwith sharpened cutting edges located in succession between the pad andthe cap, at least one of the guard and the cap being movable against aspring force, in response to a user bringing the razor blade unit intocontacting relation with skin to be shaved but prior to beginning ashaving stroke generally parallel to the skin, from an at-rest positionunloaded by externally applied forces to a predetermined operabledepressed position in which a target blade geometry is obtained, thethree blades being independently mounted for spring-biased movement sothat during shaving the blade movement from respective operablepositions is translational without changing respective blade angles,wherein when said first and third blades are depressed by an equalamount, the force exerted on said first blade is less than the forceexerted on said third blade, and wherein in the at-rest position theblade edges are disposed below a plane tangential to the skin contactingsurfaces of the guard and the cap.
 49. A shaving cartridge comprising ahousing having connecting structure adapted to make a connection to ahandle, a guard at the front of the cartridge, a cap at the back of thecartridge, and first, second and third parallel blades each withsharpened skin-contacting cutting edges located on said housing, betweensaid guard and said cap and independently mounted for spring-biasedmovement with respect to said housing, said third blade being nearer thecap than is said first blade, said blades being movable against thespring bias, in response to a user bringing the razor blade unit intocontacting relation with skin to be shaved wherein skin contactingsurfaces of the guard, cap and three blades bear on the surface to beshaved, from at-rest positions unloaded by externally applied forces todepressed start-shaving positions wherein a target blade geometry isattained in which the exposure on the first blade is less than zero andthe exposure on their blade is greater than zero, the three blades beingmounted so that during shaving the blade movement from respectiveshaving position is translational without changing respective bladeangles, and wherein when said first and third blades are depressed by anequal amount, the force exerted on said first blade is less than theforce exerted on said third blade.
 50. The cartridge of claim 49,wherein in said shaving positions the exposure on the first blade isless than or equal to the exposure on the second blade, and the exposureon the second blade is less than or equal to the exposure on the thirdblade.
 51. A safety razor blade unit according to claim 49, wherein inthe at-rest positions the third blade has a more positive exposure thanthe first blade.
 52. A shaving razor comprising a handle, a housingconnected to said handle, a guard at the front of the cartridge, a capat the back of the cartridge, and first, second and third parallelblades each with sharpened skin-contacting cutting edges located on saidhousing between said guard and cap and independently mounted forspring-biased movement with respect to said housing, said third bladebeing nearer the cap than is said first blade, said blades being movablefrom initial at-rest positions determined by respective exposures of theblades to shaving positions, the three blades being mounted so thatduring shaving the blade movement from respective shaving positions istranslational without changing respective blade angles, wherein whensaid first and third blades are depressed by an equal amount the forceexerted on said first blade is less than the force exerted on said thirdblade.
 53. A safety razor blade unit according to claim 52, wherein inthe at-rest positions the third blade has a more positive exposure thefirst blade.
 54. The shaving razor of claim 52, wherein said housing isconnected to said handle by a pivot is closer to said guard than it isto said cap.